Endoscopes are commonly used to view the interior passage of an object. Endoscopes have industrial applications wherein the endoscope is used to view a passage within, for example, a piece of equipment. Endoscopes also have medical applications wherein the endoscope is used to view a passage within the body of a patient.
An endoscope typically includes an endoscope body and optical components carried by the endoscope body to enable viewing of the passage distally of the distal end of the endoscope body. The optical components may also include illumination optics for illuminating the field of view, and such illumination optics may comprise optical fibers carried by the endoscope body.
The optical components also include the optics necessary to transmit or relay an image proximally and to provide the image to an eyepiece for direct visualization or to a camera which enables viewing of the scene on a T.V. monitor. These latter optics may include an objective for providing an image plane, eyepiece optics adjacent the proximal end of the endoscope body and an elongated fiberoptic image guide in the endoscope body for transmitting the image proximally to the eyepiece optics.
One problem with endoscopes of the type that includes an image guide is the field curvature introduced by the objective. It is often desirable for the objective to provide a relatively wide field of view, and this, in turn, tends to create field curvature. Consequently, the image plane formed by the objective is curved, and if the curved image plane is not properly accommodated, the image guide transmits an image that is partly out of focus to the eyepiece optics.
In an attempt to solve this problem, Yamagata U.S. Pat. No. 4,874,220 discloses an endoscope which provides a curved image plane spaced from the objective and a curved end surface on the image guide. The curvature of the end surface of the image guide substantially conforms to the curved image plane of the objective and is substantially located at the image plane. This is done for the purpose of attempting to form an image on the curved end surface of the image guide with all points of the image in focus. However, the refraction which occurs at the air-optical fiber interface tends to create dark regions in the image. Specifically, this tends to occur at locations where the end faces of the individual optical fibers of the image guide are at an angle with respect to the light rays which they receive.
Kitano et al U.S. Pat. No. 3,666,347 discloses an optical system having optical fibers which are curved to present end faces which are essentially normal to a curved image plane. Although this tends to reduce the problem of dark spots referred to above, curving the optical fibers in this fashion increases the cost and complexity of the structure. Published Japanese Patent Application No. 48(1973)-24742 also discloses an image guide with a curved end surface for accommodating a curved image plane. However, the image guide is spaced from the objective lens by a gap and in one embodiment the optical fibers are curved in the manner described above in connection with Kitano et al thereby introducing similar cost and complexity problems.